1. Field of the Invention
The present invention relates to burners and lances for use in melting metals, such as ferrous materials in electric arc furnaces.
2. Related Art
The melting process in an electric arc furnace is a semi-batch process where cold raw metal, typically scrap metal, is loaded by means of a basket or bucket two to four times per melting process.
The electric arc melting processes and the advantages of oxygen use therein are discussed in the article “Efficiency of oxygen technologies in the EAF” by M. Grant and B. Allemand, and published in AISE Electric Arc Furnace Conference Proceedings, 2000.
The process for melting metal in an electric arc furnace (hereafter referred to as the “melting process”) essentially comprises two steps:                a melting step, and        a refining step.        
During the melting step, raw solid metal is loaded into the furnace and heat is supplied to the raw solid metal in the furnace so as to preheat and melt the metal. This heat is provided, on the one hand, via the electrodes or phases of the electric arc furnace and, on the other hand, by one or more burners mounted in the electric arc furnace, the flame of which is directed to the raw solid metal. When a new bucket- or basketload of raw metal is added to the electric arc furnace, the melting step is continued in order to melt the newly added raw metal.
Only a limited number of burners can be installed in an electric arc furnace, typically four per furnace shell.
In general, burners are installed:                between phases on an AC (Alternating Current) furnace,        near the slag door, and        near the sump.        
At the end of the melting step, when substantially all raw solid metal has melted, the molten metal is subjected to a refining step. During the refining step, the molten metal is refined so as to achieve the desired composition thereof. Typically, a supersonic jet of oxygen is used to penetrate the slag and decarburize the molten steel. The refining step usually also includes a foaming slag process in which oxygen and pulverized coal are injected together to produce foaming slag.
The use in new and revamped electrical arc furnaces of multi-function tools, combining a burner and a supersonic lance in a single apparatus, is gaining increasing acceptance.
In known multi-function tools the burner and the lance equipped with a convergent-divergent nozzle are combined in co-axial arrangement. Such known multi-function tools are commercialized by the applicant under the commercial denomination PyreJet™.
As with conventional, non-multi-function tool burners, the burner of the multi-function tool is used for preheating and melting the raw metal, in particular scrap, following the introduction of each bucketload of raw metal. The burner also makes it possible to avoid or eliminate cold areas in the furnace.
The main purpose of the lance is to create a supersonic flow so that the resulting focused oxygen jet is able to penetrate the slag and decarburize steel during refining. When the multi-function tool is further equipped with means to inject pulverized coal, the lance can also be used in combination with coal injection to create foamy slag during refining.
Although the use of known multi-function tools in electric arc furnaces have already led to a significant increase in energy efficiency of the electric arc furnace melting processes, there remains a need to achieve even higher energy efficiency by reliable means.
It has been shown that the best orientation for the supersonic nozzle/for the supersonic oxygen jet during refining in the electric arc furnace is in the range of about 40° to about 45° with respect to the molten bath, i.e. with respect to the horizontal plane.
The best inclination for the burner/for the burner flame during the melting step has been found to be usually about 20° with respect to the horizontal plane.
Consequently, in view of the co-axial arrangement between the burner and the lance in known multi-function tools a compromise between these two optimum ranges has been required. Usually, the optimum inclination of the supersonic nozzle/supersonic oxygen jet has been considered to take precedence over the optimum inclination of the burner/flame, and known multifunction tools are usually installed with an angle of about 45°.
Known multi-function tools therefore present the inconvenience that the burner is not installed according to its optimum inclination and that therefore heating efficiency of the multifunction tool during the melting step is impaired when compared to a conventional non-multi-function tool burner with the optimum burner inclination.
Furthermore, an important factor in melting processes in electric arc furnaces is the evolution of scrap or raw metal pile geometry during the melting step. As the melting proceeds, the level of the pile of raw solid metal decreases. On the other hand, when a new bucketload of raw metal is added to the electric arc furnace, the level of the pile of raw solid metal in the furnace suddenly increases.
As, in known multi-function tools, the burner has a fixed position and inclination, the position of the burner and the orientation of the burner and burner flame is again a compromise, without active response to the changes in the raw metal pile geometry, and again, the heating efficiency of the burner is thereby impaired.
From US-A-2003/0075843, it is known to actuate or pivot a multi-functional tool in an electric arc furnace by mechanical means. This approach is not durable in highly polluted environments such as occur in electric arc furnaces, because the moving parts are then subjected to severe mechanical and chemical attacks.
It is an object of the present invention further to increase the energy efficiency of melting processes in electric arc furnaces.